4.6L General DiscussionThis section is for non-tech specific information pertaining to 4.6L (Modular) Mustangs built from 1996 to 2004.

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offroad h pipe and loss of low end. Yeah..I know it's been covered.

I just installed my offroad h pipe and flowmaster american thunder catback system on my car. I got a great deal from a guy who was selling a pile of aftermarket mustang stuff since he sold his car. I will say that it does sound excellent. I'm not sure if I want to keep it on there since there was such a noticable loss of low end power. I've read a handful of forums on this and there is some debate, but this is not debatable. I could two hours earlier stomp on the throttle in first just about anywhere and break the tires loose, and sometimes in second. Now it just pukes and eventually livens up and goes pretty good. I do think there is some top end performance gains.

To be fair I wasn't aware I would extensions for the front o2 sensors and those regulate air fuel mixture and could be throwing things way outta wack. I will have them tomorrow to see for sure.

I'm looking for feedback from anyone who's been in this predicament, do I put in a set of aftermarket cats and split the difference between sound and low end? Is there really anything other than major internal work that will bring back the low end torque I'm already starting to miss, or ditch the H pipe and go back to a good ol' stocker? Thanks!

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I just installed my offroad h pipe and flowmaster american thunder catback system on my car. I got a great deal from a guy who was selling a pile of aftermarket mustang stuff since he sold his car. I will say that it does sound excellent. I'm not sure if I want to keep it on there since there was such a noticable loss of low end power. I've read a handful of forums on this and there is some debate, but this is not debatable. I could two hours earlier stomp on the throttle in first just about anywhere and break the tires loose, and sometimes in second. Now it just pukes and eventually livens up and goes pretty good. I do think there is some top end performance gains.

To be fair I wasn't aware I would extensions for the front o2 sensors and those regulate air fuel mixture and could be throwing things way outta wack. I will have them tomorrow to see for sure.

I'm looking for feedback from anyone who's been in this predicament, do I put in a set of aftermarket cats and split the difference between sound and low end? Is there really anything other than major internal work that will bring back the low end torque I'm already starting to miss, or ditch the H pipe and go back to a good ol' stocker? Thanks!

ive never heard of anyone noticing a HUGE difference. some people say its very minimum/negligible. Did you tune the car for the offroad pipe? If the a/f ratio is off it will throw things outta wack.

As i was typing my thread i was thinking man...you unplugged your feont o2 sensors and you think it will run normal? Knock knock puddin head.. i soldered extensions cleared the cel and will take it out once i get these kids to bed. Mustangs sound the best!

Also make sure you don't have any type of exhaust leak. My last off road set up had a messed up gasket at the passenger side header where the midpipe bolts up. It wasn't noticeable until I uninstalled it. Also I had a problem once where the driver side would loosen enough to form a leak, where you could actually hear it. That made for a huge loss in low end power.

Yeah I birdshi** welded the exhaust because the fitment was so terrible, and I suspect the passenger side flange at the manifold is leaking. I extended the front o2 sensors soldering longer wires in place and wrapped them. It works for about a day then the ses light comes back on, probably due to the leaks. I'm done, my mechanic owes me money for spray foaming his addition so it's going in the shop tomorrow.

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